1. Field of the Invention
The present invention relates to an electronic device such as a transmitter-receiver unit in a portable telephone provided with heat generating components.
2. Description of the Related Art
A conventional electronic device will now be described with reference to FIG. 2, which is an exploded perspective view showing principal portions of a conventional electronic device.
As shown in FIG. 2, a frame 11 is formed in a rectangular box shape by molding using an insulating synthetic resin material. The frame 11 comprises side walls 11b which define the rectangular shape and a bottom wall 11a of a rectangular shape which partitions the inside space formed by the side walls 11b into upper and lower space portions. The upper space portion serves as a receptacle portion 11g which is open upward and the lower space portion serves as a vacant space portion 11h which is open downward.
Retaining portions 11f extending downward are formed respectively at lower end portions of opposed side walls 11b. Further, a metallic film (not shown) is formed on the whole surface of the frame 11 by plating for example.
A printed wiring board 12 is a flat board of a generally rectangular shape, with wiring patterns 12a of a desired shape being formed on one or both sides of the board 12. The printed wiring board 12 is mounted to the receptacle portion 11g of the frame 11 by a suitable means and is held therein.
Heat generating components 13, which are power transistors for example, each have a body portion 13a of a rectangular shape and a plurality of terminals (not shown) projecting outward from side walls of the body portion 13a.
The body portion 13a of each heat generating component 13 is put on the printed wiring board 12 and the terminals (not shown) are soldered to the wiring patterns 12a on the board 12, whereby the heat generating component 13 is installed on the printed wiring board.
A plurality of heat radiating members 14 are each formed by cutting and bending a metallic plate. The heat radiating members 14 each comprise a base portion 14a which is in the form of a rectangular flat plate, a U-shaped arm portion 14b extending upward from the base portion 14a, and a mounting portion 14c extending from the arm portion 14b, with a hole 14d being formed in the mounting portion 14c.
The plural heat radiating members 14 are mounted onto the printed wiring board 12 each individually by inserting a screw (not shown) through the hole 14d of the mounting portion 14c threadedly into the printed wiring board 12. This mounting operation is performed in such a manner that the lower surface of the base portion 14a comes into abutment against the upper surface of the body portion 13a of the associated heat generating component 13. The heat generated from the heat generating component 13 is radiated through the heat radiating member 14.
A mother board 16 is formed in the shape of a flat plate using an insulating resin material. Electronic components are mounted thereon such as a memory unit for storing telephone numbers and an arithmetic unit for carrying out various arithmetic operations. The frame 11 is put on the mother board 16 and secured to the same board by its retaining portions 11f.
In the conventional electronic device, however, since the heat radiating members for radiating the heat generated from heat generating components are mounted with screws or the like to the printed wiring board, the board is required to have a plurality of mounting portions such as tapped holes for mounting the plural heat radiating members, with consequent increase in size of the board, that is, increase in size of the electronic device. Besides, the screw tightening operation is required at every mounting of each heat radiating member, thus giving rise to the problem that the number of working steps increases.
Another problem is that if the heat radiating members are provided so as to have a sufficient heat radiating area, an increase in size of the same members results, with consequent increase in size of the electronic device.